Sheep grazing can be a very effective way of terminating cover crops, providing it is well managed and planned carefully to avoid creating problems, latest research at Farmacy’s demonstration site in Lincolnshire shows.
Trials this winter at Redhouse Farm, Waddingworth, highlighted the importance of a well-managed grazing regime for effectively removing cover crop residues ahead of spring drilling, while returning valuable nutrients to the soil and encouraging microbial activity.
As Farmacy agronomist Alice Cannon told growers at a recent open day at the site, getting the grazing strategy wrong risked damaging soil structure and potentially left uneven residues, all of which could compromise following crop establishment.
Species mix must also be selected carefully to ensure cover crops suited sheep grazing, while still delivering their other desired functions, such as structural soil improvement or fertility building, she said.
The cover crop trial at Redhouse Farm involved three main areas:
Un-grazed vetch oats and phacelia
Grazed forage rape, rye and vetch
Grazed stubble turnip, forage rye and turnip rape.
The grazed areas were both 2.5ha blocks, fenced off with electric fencing, and grazed by 100 ewes over the whole 5ha area. All cover crops were desiccated with glyphosate in early March.
Farmacy agronomist Rebecca Creasey said that while grazing effectively terminated the cover crops, poaching and shallow compaction around tracks and water troughs was an issue on the heavier soils last winter, exacerbated by the site’s high water table.
Careful timing to avoid grazing in very wet conditions and a more intensive, “short, sharp” grazing regime could have helped overcome the poaching issues, she suggested. More use of strip grazing, where sheep are restricted to certain parts of the field until cover is cleared before being moved on to a fresh area, was of particular interest.
“The ideal would be to have more sheep, say 500-600 ewes, per 5ha area for 5-7days maximum before being moved on to ensure even grazing without poaching.
“If that’s not possible, strip grazing fewer sheep on a smaller area, say 100 ewes on 1ha, could help get the same effect.”
Miss Cannon said grazing could occur at any time providing conditions allowed, although post-winter was most common, and after 15th January if cover was an Ecological Focus Area (EFA) mix.
Careful consideration must be given to species and varietal selection for any cover crop mix, especially if planning to graze with sheep, Miss Cannon advised.
Buckwheat for example, was poisonous to sheep, while phacelia was undesirable to sheep although they would still eat it, she said.
“In the past stubble turnips have traditionally be used in grazing mixes, but that won’t necessarily work in a short, intensive grazing system, as there isn’t always enough time for sheep to eat the roots before they’re moved on.”
She preferred a three-way mix based on legumes and cereals. “Cereals are quick to establish, give good top growth for grazing and have fibrous roots that benefit the soil. Regrowth also provides extra grazing material.
“Legumes offer excellent root anchorage and nitrogen fixation for the soil, and are also a good source of protein for grazing animals.”
Deciding when to terminate cover crops depended on several factors, and chief among them was water management, Miss Cannon said.
Leaving cover green for longer allowed roots to draw more water from deeper in the soil over winter, although potentially created challenges for establishing the following crop, as green surface material needed time to dry out if cover had not been removed by grazing.
In contrast, earlier termination reduced the risk of drilling into a layer of wet, decaying biomass, but could mean the underlying soil was wetter as roots had not been extracting soil moisture for as long, she noted.
There was also the issue of nitrogen lock-up to consider. High-carbon cover crops (e.g. brassicas with more fibrous stem content) could potentially temporarily lock-up nitrogen so that it was not immediately available to the following crop, making it more important to “front-load” fertiliser applications in spring crops, Miss Cannon explained.
“When cover crops have been used for typically five-plus years [exact times vary depending on soil type and health]the nutrient imbalance is naturally redressed, allowing a return to more normal nitrogen timing.
“Nitrogen lock-up is less of an issue when cover crops are grazed as nitrogen in manure is more readily available.”
Growers also had to be wary of potential allelopathy when oats or rye were in the mix, which could delay growth in a following spring barley crop, she said. “If you’re spraying cover off with glyphosate and have more than 60% cereals in the mix, you need to be desiccating at least six weeks before drilling.”
Tips for establishing spring barley after cover crops
Desiccate well in advance to avoid allelopathy and allow time for residues to dry out and start breaking down if using a cereal-heavy cover crop
Check for compaction and take remedial action to the appropriate depth if needed
Wait for soils to dry out enough to allow good tilth creation – maximises seed-to-soil contact and ensures drilling ‘slot’ closes properly
Increase seed rate to compensate for lower tillering and potentially lower establishment in spring – aim to sow 450-500 seeds/m2 depending on conditions
Maximise nutrition during the key establishment phase by using a nutritional seed dressing, and applying seedbed phosphorus and early nitrogen. Consider splitting nitrogen application 70-30 between drilling and once the crop is emerged, rather than 50-50.
Aside from the Farmacy trials, cover crops are proving their worth for facilitating spring cropping elsewhere at Redhouse Farm.
It is the third year of using them and farm manager Ed Pritchard said that along with a concerted effort to improve field drainage and cultivation strategy, they had greatly benefitted soil condition and helped dry soils out over winter, allowing more timely spring drilling.
This was starkly highlighted in the tricky conditions last season when half of the heavy land was cover cropped over winter and the remainder left cultivated. “We managed to drill spring linseed on all land that had been cover cropped, but could never get on to the cultivated land which had to be left fallow.
This season, some 80ha of land destined for spring oats was sown with the farm’s own mix of white mustard, crimson clover and phacelia straight after harvest using a Tillso cultivator with Ultralite tines and seeder unit.
“We spray cover off two weeks before drilling spring crops straight into the residue using our Vaderstad Rapid.”
Mr Pritchard was encouraged by the results of Farmacy’s cover crop trial and suggested that sheep grazing could be the way he would like to go with cover crop termination in future.
350ha family farm
Predominantly growing winter combinable crops (first wheat and oilseed rape)
Also 80ha of spring oats in 2019
Cover crops grown to condition soil ahead of spring cropping.